High-strength joint and fastener assembly therefor

ABSTRACT

A high-strength joint and fastener assembly therefor wherein an internally tapered sleeve is placed within substantially aligned bores in mating structural members and a tapered bolt is inserted through the members and into the internally tapered sleeve. A threaded fastener member, such as nut, is threaded on the end of the tapered bolt and is tightened to place a load on the joint thereby radially expanding the tapered sleeve outwardly within each of the bores in the structural members to compensate for variations in the holes due to out of roundness of the holes, misalignment between holes in each structural member, or variations in hole diameter tolerances.

trite tts aterrt 1 eme [72] Inventor lltoger 111B. Whitesdde 2,972,2752/1961 Baubles 85/83 Cirilnrtou, lllurlingtnn, NJ. 3,099,470 7/1963ZumbuschW. 287/127 [21] Appl. No. 7941,1123 3,270,410 9/1966 Salter eta1 ...287/l89.36 FX [22] Filed 11mm. 27, 1969 3,293,725 1/1967 Boteler287/l89.36 F [45] Patented Eent. 7, 119711 FOREIGN PATENTS [73] fiifi fifi mf SW13 1,452,293 8/1966 France 85/83 Primary Examiner-David JWilliamowsky Assistant Examiner-Wayne L. Shedd 1 MHGH"STMEWGTM JmHMT ANDWASTFENEM /ltt0rneys-Stanley Belsky and Curtis, Morris and SaffordfltSSlEll/llfillt' 'llllllfillllllill lllll l d Cluilms, 3 Drawing Figs.

[52] 11. .5. 1:11 ..2l37/l1$9.31@, AMTRACT A hightrength joint andfastener assembly 85/35 therefor wherein an internally tapered sleeve isplaced within [5 1 1 lnt. C1 1 16b 9/00 b ta tiall ali ed bore in matingstructural members and a [50] ll llelld all Search 287/189.36 ta d bolti ins rted through the members and into the in- F, 20-92 E, 127, 1 1 l1316- ternally tapered sleeve. A threaded fastener member, such as 235/33, 35 nut, is threaded on the end of the tapered bolt and istightened to lace a load on the 'oint thereby radially expanding the1561 mwfl tap red sleeve outwardly within each of the bores in thestruc- UNITED STATES PATENTS tural members to compensate for variationsin the holes clue to 591,193 10/1897 Osgood 277/220 X out of roundnessof the holes, misalignment between holes in 1,323,192 1 1/1919liottusch. 277/220 each structural member, or variations in holediameter 2,604,974 7/1952 Daigle 287/1 1 1 UX tolerances.

PATENTEU SEP 7 I87! INVENTOR. ROGER B. WHITESIDE 6%, m4 iw ATTORNEYSspasms This invention relates to high-strength joints and moreparticularly to high-strength joints and fastener assemblies thereforwherein a fastener is adapted to pass through aligned openings in thestructural members to be joined to tightly clamp the members together.

In precision fastening applications, i.c., in aircraft, missile andspace applications, wherein it is necessary to form a joint of two ormore structural members, such as sheets or plates of metal, it isessential that the joint be formed with maximum structural integrity toyield the highest tensile and shear strength characteristics which canbe obtained from the materials employed. Most commonly, such jointsconsist of two or more structural members placed in abutting face-tofacerelationship with each of the members having substantially aligned borestherein and a headed fastener member, such as a bolt or rivet, is placedtherethrough and suitably engaged on its other end to apply acompressive load to the structural members thereby to tightly clamp themembers together.

ideally, the bolt should fit in the bores of the structural members astightly as possible such that when the compressive load is applied tothe fastening member, the walls of the bores containing the fasteningmember are actually stressed. in fact, the greatest possible strength insuch joints, is achieved when the fastener member engages the wall ofthebores in the structural members throughout the entire periphery of thebolt and throughout the full length of the bolt. Practically, results ofthis type are difficult to achieve as it is necessary to maintaincritically high tolerance limits for bore sizes in the structuralmembers, degree of roundness of the bores, surface finish of the wallsof the bore as well as critical tolerance requirements for the diameterof the bolt, surface finish of the periphery of the bolt and the like.To compound the already difficult task of achieving the tolerance rangesnoted above, it is also necessary to insure precise alignment of thebores in mating structural members in order to create, in effect, aunitary constant dimension bore when the structural members are placedin abutting face-to-face relationship.

Maintenance of such critical tolerances is prohibitive with all thevariable factors that must be considered both from a cost factor andfrom the time and effort involved in trying to drill, bore and reamholes to the tolerances required as well as machining bolts and rivetsto the same precise tolerances.

it is, therefore, an object of the present invention to provide a jointand fastener assembly therefor to withstand the maxr imum possiblestress limits inherent for the particular materials employed.

it is a further object of the present invention to provide a joint andfastener assembly therefor utilizing the maximum practical bearingsurface of the interior wall surface of the bores in the structuralmembers to be joined.

It is also an object of the present invention to provide ajoint andfastener assembly therefor which reduces stress concentration andfatigue in the structural members to be joined by imparting a uniformradial stress to the walls of the bores in the structural members.

Another object of the present invention is to provide a highstrengthjoint and fastener assembly therefor without requiring or necessitatingcostly manufacturing procedures.

in a preferred embodiment of the present invention, a tapered fastenermember such as a bolt is used within a tapered sleeve which is placedwithin substantially aligned bores in mating structural members. Thesleeve includes a scarfed step joint thereby to facilitate radiallyoutward expansion of the sleeve as the bolt is loaded, for example bytightening a nut thereon. The scarfed step joint in the tapered sleeveassures uniform radial expansion of the sleeve in the receiving boresthereby to fill the bores in the structural members and apply a uniformradial stress along the internal wall periphery.

Additional and further objects and advantages will become readilyapparent when considered with the following descrip tion with referenceto the accompanying drawings wherein:

FIG. l is an exploded perspective view showing the tapered bolt, taperedsleeve, structural members to he joined and a nut;

FIG. 2 is a vertical sectional view showing an assembled joint; and

FIG. 3 is a horizontal sectional view taken on line 3-3 of H6. 2. Withreference to the drawings and particularly FIG. ll, there is shown abolt having a driving head 12, which may be of any standardconfiguration but is shown here illustratively as a hexagonal-shapedhead, a tapered shank portion M and a standard threaded end portion16.1% sleeve 18 having a cylindrical exterior surface is adapted to beplaced within substantially aligned bores 20 and 221 of structuralmembers 2 1i and 26, respectively. Sleeve llfl includes an internallytapered surface 28 which is complimentary to the taper on the taperedshank portion M of bolt lltl. Sleeve llh also includes a longitudinallydisposed scarfed step joint 30 which permits the sleeve 18 to expandradially outwardly after it is placed within the bores 20 and 22. Athreaded fastener member such as a nut 32, which can be of any standardnut configuration, having an internally threaded surface 34 to receiveand coact with an externally threaded surface 16 of bolt ll) completesthe assembly.

As best seen in FIG. 2, the completed joint includes the abuttingstructural members 24 and 2b with their respective bores 20 and 22 beingsubstantially coaxially aligned. Internally tapered sleeve 18 is placedtherein and the bolt 110 is placed within sleeve it! with the taperedshank portion 14 positioned within tapered portion 2d. The nut 32 isthen threaded on the end to of bolt ill and tightened to place anaxially compressive load which clamps structural members 24 and 26together.

As best seen in H6. 3, the scarfed step joint 30 includes arcuateabutting finger extensions as and 38 with each finger ex tension havingapproximately one-half the thickness of sleeve l8. Finger as has an endportion W which, before any load is placed on sleeve lib, abuts shoulderportion 42 formed by the extension of finger 33 from the main sleeveportion. Similarly, finger 38 includes an end portion 44 which initiallyabuts a shoulder portion lb formed by the extension of finger as fromthe main sleeve portion.

As noted above, sleeve lb initially has a substantially cylin' dricalexterior periphery due to the closely nesting relationship of thefingers as and 3d and is selected for a particular ap plication so thatthe outer diameter of the sleeve provides a sliding fit within bores 2dand 22. The particular shape of the scarfed step joint Elli permits aradial expansion of the sleeve 112i when the bolt it) moves axiallywithin the sleeve the nut 32?. is tightened thereon. Axial movement ofbolt ll) imparts a radially outward force vector uniformly throughoutthe tapered interior surface 2%} of the sleeve which expands the sleeveto completely full bores Eli and Since the degree of radial expansion isnot of a great magnitude, the sleeve ill may be constructed fromrelatively hard material having a somewhat limited ductility and,because the material of the sleeve is hard, the ultimate stress ratingof the joint is greatly increased. The expansion of sleeve litl is alsoeffective when the bores 20 and 22 are slightly misaligned as the sleeveductility permits a nonuniform expansion in each bore.

Prior art attempts to provide joints of this type have used taperedbolts and tapered sleeves but have relied on a softer sleeve material ofgreater ductility to permit sufficient radial expansion of the sleeve.Thus, the sleeve material used in these devices must be softer and moreductile to achieve the same degree of peripheral load bearing surfacewithin the bores of the structural members. Other devices have used axial, closed end slots within the sleeve and these slots are relativelycostly to machine and result in significantly less peripheral loadbearing surface in contact with the internal wall surface of the boresthereby resulting in reduced joint integrity. Additionally, the slotsmust be stretched in order to expand the sleeve radially outwardly whichresults in portions of the sleeve being of nonuniform thickness and,hence, causing a nonuniform variation in load stress concentrations inthe joint.

The sleeve of the present invention can be readily manufactured in aflat stock condition and then rolled to form an ex terior cylindricalsleeve surface thereby simplifying manufacture and reducing costs.Additionally, the completed cylindrical sleeve can be hardened andplated after it has been rolled.

It is thus seen that the present invention provides a tapered sleevewhich can be radially expanded outwardly within aligned bores of two ormore abutting structural members thereby to increase and maximize theperipheral bearing surface of the joint while stressing the internalwall surface in the structural members to maximize the strength of thejoint.

What is claimed is:

1. In a high-strength joint comprising at least two structural memberswith substantially aligned bores therein, a sleeve of relatively hardmaterial having a limited ductility, said sleeve having a cylindricalexterior surface and a tapered internal surface and extending throughoutthe length of said aligned bores, a bolt having a driving head and ashank, said shank including a tapered segment having a tapercomplimentary to said sleeve internal taper and a threaded end portion,a threaded fastener member adapted to coact with said bolt threaded endportion, the improvement wherein:

said sleeve includes a single longitudinally disposed expandable jointextending throughout the longitudinal extent of said sleeve to allowsaid sleeve to expand radially outwardly within the confines of saidaligned bores in said structural members when said joint is loadedthereby to impart a uniform stress to the wall surfaces defining saidbores, said expandable joint comprising a scarfed step joint wherein apotion of said sleeve overlaps another portion of said sleeve inface-to-face abutting relationship.

2. In a high-strength joint comprising at least two structural memberswith substantially aligned bores therein, a sleeve having a cylindricalexterior surface and a tapered internal surface within said alignedbores, a bolt having a driving head and a shank, said shank including atapered segment having a taper complimentary to said sleeve internaltaper and a threaded end portion, a threaded fastener member adapted tocoact with said bolt threaded end portion, the improvement wherein:

said sleeve includes a single longitudinally disposed expandable jointto allow said sleeve to expand radially out wardly within the confinesof said aligned bores in said structural members when said joint isloaded thereby to impart a uniform stress to the wall surfaces definingsaid bores, said expandable joint comprising a scarfed step jointwherein a portion of said sleeve overlaps another portion of said sleevein face-to-face abutting relationship, said overlapping portions of saidjoint comprising arcuate finger extensions of said sleeve, each saidextension being of the order of one-half the thickness of the sleeve andhaving a radius of curvature coincident with the radius of curvature ofsaid sleeve at that point.

3. A fastener assembly for a high-strength joint comprising a bolthaving a driving head, a shank threaded at its end, said shank includinga tapered midportion having a generally frustoconical configuration withthe wider end adjacent said driving head and the narrower end adjacentsaid threaded end, an internally threaded nut adapted to engage andcoact with said threaded end, and a sleeve member of relatively hardmaterial having a limited ductility, said sleeve having a generallycylindrical exterior and a frustoconical internal surface complimentaryto the frustoconical portion of said bolt shank, said sleeve extendinglongitudinally throughout the frustoconical portion of said bolt shankand further including a longitudinally disposed expandable jointextending throughout the longitudinal extent of said sleeve thereby topermit a uniform radially outward expansion of said sleeve when said nutis progressively engaged on said bolt while said bolt is positionedwithin said sleeve, said expandable joint comprising overlapped arcuateextensions of the wall of said sleeve.

4. A fastener assembly for a high-strength joint comprising a blothaving a driving head, a shank threaded at its end, said shank includinga tapered midportion having a generally frustoconical configuration withthe wider end adjacent said driving head and the narrower end adjacentsaid threaded end, an internally threaded nut adapted to engage andcoact with said threaded end, and a sleeve member having a generallycylindrical exterior and a frustoconical internal surface complimentaryto the frustoconical portion of said bolt shank, said sleeve furtherincluding a single longitudinally disposed expandable joint thereby topermit a uniform radially outward expansion of said sleeve when said nutis progressively engaged on said bolt while said bolt is positionedwithin said sleeve, said expandable joint comprising overlapped arcuateextensions of the wall of said sleeve, each said arcuate extensionhaving a thickness approximately equal to one-half the wall width of thesleeve,

1. In a high-strength joint comprising at least two structural memberswith substantially aligned bores therein, a sleeve of relatively hardmaterial having a limited ductility, said sleeve having a cylindricalexterior surface and a tapered internal surface and extending throughoutthe length of said aligned bores, a bolt having a driving head and ashank, said shank including a tapered segment having a tapercomplimentary to said sleeve internal taper and a threaded end portion,a threaded fastener member adapted to coact with said bolt threaded endportion, the improvement wherein: said sleeve includes a singlelongitudinally disposed expandable joint extending throughout thelongitudinal extent of said sleeve to allow said sleeve to expandradially outwardly within the confines of said aligned bores in saidstructural members when said joint is loaded thereby to impart a uniformstress to the wall surfaces defining said bores, said expandable jointcomprising a scarfed step joint wherein a potion of said sleeve overlapsanother portion of said sleeve in face-to-face abutting relationship. 2.In a high-strength joint comprising at least two structural members withsubstantially aligned bores therein, a sleeve having a cylindricalexterior surface and a tapered internal Surface within said alignedbores, a bolt having a driving head and a shank, said shank including atapered segment having a taper complimentary to said sleeve internaltaper and a threaded end portion, a threaded fastener member adapted tocoact with said bolt threaded end portion, the improvement wherein: saidsleeve includes a single longitudinally disposed expandable joint toallow said sleeve to expand radially outwardly within the confines ofsaid aligned bores in said structural members when said joint is loadedthereby to impart a uniform stress to the wall surfaces defining saidbores, said expandable joint comprising a scarfed step joint wherein aportion of said sleeve overlaps another portion of said sleeve inface-to-face abutting relationship, said overlapping portions of saidjoint comprising arcuate finger extensions of said sleeve, each saidextension being of the order of one-half the thickness of the sleeve andhaving a radius of curvature coincident with the radius of curvature ofsaid sleeve at that point.
 3. A fastener assembly for a high-strengthjoint comprising a bolt having a driving head, a shank threaded at itsend, said shank including a tapered midportion having a generallyfrustoconical configuration with the wider end adjacent said drivinghead and the narrower end adjacent said threaded end, an internallythreaded nut adapted to engage and coact with said threaded end, and asleeve member of relatively hard material having a limited ductility,said sleeve having a generally cylindrical exterior and a frustoconicalinternal surface complimentary to the frustoconical portion of said boltshank, said sleeve extending longitudinally throughout the frustoconicalportion of said bolt shank and further including a longitudinallydisposed expandable joint extending throughout the longitudinal extentof said sleeve thereby to permit a uniform radially outward expansion ofsaid sleeve when said nut is progressively engaged on said bolt whilesaid bolt is positioned within said sleeve, said expandable jointcomprising overlapped arcuate extensions of the wall of said sleeve. 4.A fastener assembly for a high-strength joint comprising a blot having adriving head, a shank threaded at its end, said shank including atapered midportion having a generally frustoconical configuration withthe wider end adjacent said driving head and the narrower end adjacentsaid threaded end, an internally threaded nut adapted to engage andcoact with said threaded end, and a sleeve member having a generallycylindrical exterior and a frustoconical internal surface complimentaryto the frustoconical portion of said bolt shank, said sleeve furtherincluding a single longitudinally disposed expandable joint thereby topermit a uniform radially outward expansion of said sleeve when said nutis progressively engaged on said bolt while said bolt is positionedwithin said sleeve, said expandable joint comprising overlapped arcuateextensions of the wall of said sleeve, each said arcuate extensionhaving a thickness approximately equal to one-half the wall width of thesleeve.